<PAGE>

                                                                 EXHIBIT 10.21

                             SILICON VALLEY BANK
                              3003 Tasman Drive
                            Santa Clara, CA 95054
                      (408) 654-1000 - Fax (408) 980-6410

     This NOTE PURCHASE AGREEMENT (the "Agreement"), dated as of August 28, 
1998, is between SILICON VALLEY BANK ("Buyer") and RADIUS INC., a California 
Corporation ("Seller"), with its chief executive office at:

<TABLE>
          <S>                    <C>
          Street Address:        460 Middlefield Road
          City:                  Mountain View
          County:                Santa Clara
          State:                 California
          Zip Code:              94303
          Phone:                 650/404-6000
</TABLE>

     1.  DEFINITIONS. In this Agreement:
          1.1 "Adjustments" is the meaning set forth in Section 7 hereof.
          1.2 "Administrative Fee" is the meaning set forth in Section 2.4 
hereof.
          1.3 "Interest" is the meaning set forth in Section 2.3 hereof.
          1.4 "Purchased Note" is that Promissory Note between Radius Inc., a 
California Corporation, and Korean Data Services, Inc., a California 
Corporation, dated August 7, 1998 in the amount of $5,200,000.00 in United 
States Currency. "Purchased Note" also includes books and records about the 
Purchased Note and proceeds from voluntary or involuntary dispositions, 
including insurance proceeds.
          1.5 "Reconciliation Period" is each calendar month of every year.
          1.6 "Reserve" is the meaning set forth in Section 2.6 hereof.
          1.7 "Related Property" is all returned or rejected goods connected 
with the Purchased Note or books and records about the returned or rejected 
goods; or proceeds from voluntary or involuntary dispositions of the returned 
or rejected goods, including insurance proceeds.
          1.8 "Schedule" is the attached schedule showing the: Purchase Date, 
Schedule of Due Dates, Face Amount of Note, Total Purchased Note and Advance 
Amount.

     2.  PURCHASE AND SALE OF NOTE.
          2.1 Sale and Purchase. On the Purchase Date, Seller sells and Buyer 
buys Seller's right, title, and interest (but none of Sellers obligations) to 
payment on the Purchased Note, (the "Note Debtor").
          2.2 Payment of Advance Amount. Buyer will pay Seller, on the 
Purchase Date, $1,100,000 (the "Advance Amount").
          2.3 Payment of Interest. On each Reconciliation Date Seller will 
pay Buyer interest at the rate of 1.25(%) percent per month of 125% the 
average daily outstanding balance of the Advance Amount during the applicable 
Reconciliation Period (the "Interest"). Buyer will deduct the accrued 
Interest from the Reserve as set forth in Section 2.6 below.
          2.4 Payment of Administrative Fee. On the Reconciliation Date 
Seller shall pay to Buyer an Administrative Fee equal to .50(%) percent of 
125% the original amount of the Advance Amount (the "Administrative Fee").
          2.5 In the event that the Advance Amount is less than One Million 
Dollars and No/100**** ($1,000,000.00) by September 30, 1998, the interest 
rate defined in Section 2.3 above will be 1.75(%) per month.
          2.6 Establishment of a Reserve. Upon the purchase by Buyer of the 
Purchased Note, Buyer shall establish a reserve. The reserve shall be the 
amount by which the face amount of the Purchased Note exceeds the Advance 
Amount on that Total Purchased Note (the "Reserve"); provided, the Reserve 
with respect to that Total Purchased Note outstanding at any one time shall 
be an amount not less than 20(%) percent of the Total Purchased Note at the 
time and may be set at a higher percentage at Buyer's discretion. The reserve 
shall be the book balance maintained on the records of Buyer and shall not be 
a segregated fund.


<PAGE>

     3.  COLLECTION, PAYMENTS AND REMITTANCES.
          3.1 Application of Payments. All Payments for the Purchased Note, 
not exceeding the Total Purchased Note plus any unpaid fees and interest (if 
any), received by Seller or Buyer, are Buyers property.
          3.2 No Obligation to Take Action. Buyer has a right, but no 
obligation, to perform Seller's obligations.
          3.3 Application of Payments. All payments in respect of the 
Purchased Note, whether received from the Note Debtor or any other source and 
whether received by Seller or Buyer, shall first be applied for the account 
of Buyer until Buyer has received full and final payment in an amount equal 
to the Advance Amount plus interest, administrative fees, expenses and 
indemnity amounts payable to Buyer hereunder, with the remaining balance, if 
any, payable to Seller.

     4.  REPURCHASE OBLIGATIONS.
          4.1 Seller's Agreement to Repurchase. Seller will, at Buyer's 
option, repurchase from Buyer the Purchased Note for a purchase price equal 
to the unpaid principal of the Purchase Note if:
               (a)  There has been any breach of warranty, representation or 
covenant in this Agreement; or
               (b)  The Note Debtor asserts any discount, allowance, return, 
dispute, defense, right of recoupement, right of return, warranty claim, or 
short payment; or
               (c)  The Purchased Note remains unpaid after October 1, 1999.

     5.  POWER OF ATTORNEY.  Seller does hereby irrevocably appoint Buyer and 
its successors and assigns as Seller's true and lawful attorney in fact, and 
hereby authorizes Buyer, regardless of whether there has been an Event of 
Default, (a) to sell, assign, transfer, pledge, compromise, or discharge the 
whole or any part of the Purchased Note; (b) to demand, collect, receive, 
sue, and give releases to the Note Debtor for those monies due or which may 
become due upon or with respect to the Purchased Note and to compromise, 
prosecute, or defend an action, claim, case or proceeding relating to the 
Purchased Note, including filing a claim or voting of such claims in any 
bankruptcy case, all in Buyer's name or Seller's name, as Buyer may choose; 
(c) to prepare, file and sign Seller's name on any notice, claim, assignment, 
demand, draft, or notice of or satisfaction of lien or mechanics' lien or 
similar document with respect to Purchased Note; (d) to notify the Note 
Debtor with respect to the Purchased Note to pay Buyer directly; (e) to 
receive, open, and dispose of all mail addressed to Seller for the purpose of 
collecting the Purchased Note; (g) to execute on behalf of Seller any and 
all instruments, documents, financing statements and the like to perfect 
Buyer's interest in the Purchased Note and Collateral; and (h) to do all acts 
and things necessary or expedient, in furtherance of any such purposes. If 
Buyer receives a check or item which is payment for both the Purchased Note 
and another receivable, the funds shall first be applied to the Purchased 
Note and, so long as there does not exist an Event of Default or an event 
that notice, lapse of time or otherwise would constitute an Event of Default, 
the excess shall be remitted to Seller. Upon the occurrence and continuation 
of an Event of Default, all of the power of attorney rights granted by Seller 
to Buyer hereunder shall be applicable with respect to the Purchased Note and 
all Collateral.

     6.  REPRESENTATIONS, WARRANTIES AND COVENANTS.
          6.1 Purchased Note--Warranties, Representations and Covenants. 
Seller represents, warrants and covenants for the Purchased Receivable:
               (a)  It is the owner with legal right to sell, transfer and 
assign it;
               (b)  The correct amount is shown in Section 1.4 and is not 
disputed;
               (c)  Payment is not contingent on any obligations or contact, 
and it has fulfilled all its obligations as of the Purchase Date;
               (d)  There are no defenses, offsets, counterclaims or 
agreements in which the Note Debtor may claim any deduction or discount;
               (e)  It reasonably believes the Note Debtor is not insolvent 
as defined in the United States Bankruptcy Code ("US Code") or the California 
Uniform Commercial Code ("UCC") and the Note Debtor has not filed or had 
filed against it a voluntary or involuntary petition for relief under the US 
Code; and


<PAGE>

               (f)  The Note Debtor has not objected to payment for or the 
quality or quantity of the subject of the Purchased Note.

          6.2  Additional Warranties, Representation and Covenants. Seller 
represents, warrants and covenants:
               (a)  Its name, form of organization, chief executive office 
and the place where the records about the Purchased Note are kept is shown at 
the beginning of this Agreement and it will give Buyer at least 10 days prior 
written notice of changes to its name, organization, chief executive office 
or location of records.
               (b)  It has not filed a voluntary petition or had filed 
against it an involuntary petition under the US Code and does not anticipate 
any filing.

     7.  ADJUSTMENTS.  If the Note Debtor asserts a discount, allowance, 
return, offset, defense, warranty claim, or the like (an "Adjustment"), Seller 
will promptly advise Buyer and, with Buyer's approval, resolve the dispute.

     8.  INDEMNIFICATION.  
          (a) If the Note Debtor is released from the payment obligation for 
the Purchased Note because of: (i) Seller's act or omission; or (ii) any of 
the documentation about the Purchased Note which results in termination of 
any of the Note Debtor's obligation for the Purchased Note, then Seller will 
pay Buyer the lesser of the Purchased Note not payable or the unpaid portion 
of the Purchased Note.
          (b)  Seller indemnifies and holds Buyer harmless from any taxes 
from this transaction (except Buyer's income taxes) and costs, expenses and 
reasonable attorney fees if Buyer promptly notifies it if any taxes of which 
Buyer has notice.

     9.  REPURCHASE EVENTS.  Any of the following is an Event of Repurchase:
          (a)  Seller fails to pay Buyer any amount when due;
          (b)  An involuntary lien, garnishment, attachment or the like is 
issued against or attaches to the Purchased Note or Related Property; and
          (c)  Seller breaches a covenant, agreement, warranty, or 
representation in this Agreement and the breach is not cured to Buyer's 
satisfaction within 10 days after Buyer gives Seller oral or written notice. 
A breach that cannot be cured is an immediate default; and
          (d)  The Note Debtor fails to pay any amount under the Purchased 
Note when due.

     10.  REPURCHASE OPTION.  When an Event of Repurchase occurs Buyer shall 
have a right to require Seller to repurchase all of the affected Purchased 
Note for a purchase price equal to the amount specified in Section 4.1. Buyer 
shall also have all rights and remedies under this Agreement and the law, 
including those of a secured party under the UCC, and the right to collect, 
dispose of, sell, lease or use all Purchased Note and Related Property.

     11.  FEES, COSTS AND EXPENSES.  Immediately on demand Seller will pay 
all reasonable fees, costs and expenses (including attorney and professional 
fees) that Buyer incurs from (a) preparing, negotiating, administering and 
enforcing this Agreement or any other agreement, including amendments, waiver 
or consents, (b) litigation or disputes relating to the Purchased Note, the 
Related Property, this Agreement or any other agreement, (c) enforcing rights 
against Seller, (d) protecting or enforcing its title to the Purchased Note 
or its security interest in the Related Property, (e) collecting any amounts 
due from Seller or for a Purchased Note under a breach of Seller's 
representation, warranty or covenant and (f) any bankruptcy case or 
insolvency proceeding involving Seller.

     12.  CHOICE OF LAW, VENUE AND JURY WAIVER. California law governs this 
Agreement.

<PAGE>

Seller and Buyer each submit to the exclusive jurisdiction of the State and 
Federal courts in Santa Clara County, California.

SELLER AND BUYER EACH WAIVE ITS RIGHT TO A JURY TRIAL FROM ANY CAUSE OF 
ACTION RELATED TO AGREEMENT, INCLUDING CONTRACT, TORT, BREACH OF DUTY OR 
OTHER CLAIM. THIS WAIVER IS A MATERIAL INDUCEMENT FOR BOTH PARTIES TO ENTER 
THIS AGREEMENT. EACH PARTY HAS REVIEWED THIS WAIVER WITH ITS COUNSEL.

     13.  NOTICES.  Notices or demands by either party about this Agreement 
must be in writing and personally delivered or sent by an overnight delivery 
service, by certified mail postage prepaid return receipt requested, or by 
FAX to the address below:

     Seller:  Radius, Inc.
              460 Middlefield Road
              Mountain View, CA 94303
              Attn: Chief Financial Officer
              FAX: (650) 404-6205

     Buyer:   Silicon Valley Financial Services/Silicon Valley Bank
              3003 Tasman Drive/NC481
              Santa Clara, CA 95054
              Attn: Credit Manager
              FAX: (408) 980-6410

     A party may change notice address by written notice to the other party.

     14.  GENERAL PROVISIONS.
          14.1 Successors and Assigns. This Agreement binds and is for 
the benefit of successors and permitted assigns of each party. Seller may not 
assign this Agreement or any rights under it without Buyer's prior written 
consent which may be granted or withheld in Buyers discretion. Buyer may, 
without the consent of or notice to Seller, sell, transfer, or grant 
participation in any part of Buyer's obligations, rights, or benefits under 
this Agreement.
          14.2 Indemnification. Seller will indemnify, defend and hold 
harmless Buyer and its officers, employees, and agents against: (a) 
obligations, demands, claims, and liabilities asserted by any other party in 
connection with the transaction contemplated by this Agreement; and (b) 
losses or expenses incurred, or paid by Borrower from or consequential to 
transactions between Buyer and Seller (including reasonable attorneys fees 
and expenses), except for losses caused by Buyer's gross negligence or 
willful misconduct.
          14.3 Time of Essence. Time is of the essence for performance 
of all obligations in this Agreement.
          14.4 Severability of Provision. Each provision of this 
Agreement is severable from every other provision in determining the 
enforceability of any provision.
          14.5 Amendments in Writing, Integration. All amendments to 
this Agreement must be in writing. This Agreement is the entire agreement 
about this subject matter and supersedes prior negotiations or agreements.
          14.6 Counter Parts. This Agreement may be executed in any 
number of counterparts and by different parties on separate counterparts and 
when executed and delivered are one Agreement.
          14.7 Survival. All covenants, representations and warranties 
made in this Agreement continue in full force while any Purchased Note amount 
remains outstanding. Seller's indemnification obligations survive until all 
statutes of limitations for actions that may be brought against Buyer have run.
          14.8 Confidential Information. Buyer will use the same degree 
of care in handling


<PAGE>

Seller's confidential information that is used for its own proprietary 
information, but may disclose information; (i) to its subsidiaries or 
affiliates in connection with their business with Seller, (ii) to prospective 
transferees or purchasers of any interest in the Agreement, (iii) as required 
by law, regulation, subpoena, or other order, (iv) as required in connection 
with an examination or audit and (v) as it considers appropriate exercising 
the remedies under this Agreement. Confidential information does not include 
information that is either: (a) in the public domain or in Buyer's possession 
when disclosed, or becomes part of the public domain after disclosure to 
Buyer; or (b) disclosed to Buyer by a third party, if Buyer does not know 
that the third party, is prohibited from disclosing the information.

SELLER:              RADIUS INC.
                     A CALIFORNIA CORPORATION

By    /s/ [illegible] 
      ---------------------------------------

Title    CFO
      ---------------------------------------



BUYER:               SILICON VALLEY BANK

By    /s/ [illegible]
      ---------------------------------------

Title    VICE PRESIDENT
      ---------------------------------------

<PAGE>

                       SCHEDULE DATED AUGUST 28, 1998
                                     TO
                           NOTE PURCHASE AGREEMENT
                         DATED AS OF AUGUST 28, 1998


SELLER:                         Radius Inc.

BUYER:                          Silicon Valley Bank

PURCHASE DATE:                  August 28, 1998

SCHEDULE OF DUE DATES:          See attached Schedule of Due Dates

FACE AMOUNT OF NOTE:            $5,200,000.00 ***USD

TOTAL PURCHASED NOTE:           $5,200,000.00 ***USD

ADVANCE AMOUNT:                 $1,100,000    ***USD



Seller warrants and represents that (a) its warranties and representation in 
the Agreement are true and correct as of the date of this Schedule and (b) no 
Event of Default has occurred under the Agreement.



SELLER:              RADIUS INC.
                     A CALIFORNIA CORPORATION

By    /s/ [illegible]
      ---------------------------------------

Title    CFO
      ---------------------------------------



BUYER:               SILICON VALLEY BANK

By    /s/ [illegible]
      ---------------------------------------

Title    VICE PRESIDENT
      ---------------------------------------


<PAGE>
                        CORPORATE RESOLUTION TO SELL

I, the Secretary or Assistant Secretary of Radius, Inc. (the "Seller"), 
certify that:

     The Seller is a California corporation, and

     Attachments 1 and 2 are copies of Seller's Articles of 
     Incorporation and Bylaws which are currently effective, and

     At a duly held meeting of Seller's directors at which a quorum was 
     present (or by other authorized corporate action) the following 
     resolutions were adopted:

          "RESOLVED THAT any (    ) of the following officers of Seller, 
          whose signatures are below:

          <TABLE>
          <CAPTION>
          Name                     Title               Signature

          <S>                      <C>                 <C>
          Mark Housley             CEO
          -----------------------  ------------------  -----------------------
          Henry V. Morgan          CFO                 /s/ Henry V. Morgan
          -----------------------  ------------------  -----------------------

          -----------------------  ------------------  -----------------------

          -----------------------  ------------------  -----------------------
          </TABLE>

          acting for Seller are authorized to:

          EXECUTE PURCHASE AGREEMENT. To enter a Note Purchase Agreement with 

          Silicon Valley Bank ("Buyer") on terms agreed by them and Buyer 
          for the sale of certain Seller's notes and to execute renewals, 
          extensions, modifications, refinancings, consolidations or 
          substitutions of any notes and to do other acts and things and 
          execute and deliver other documents that they consider necessary to 
          carry out the effect of these Resolutions.

          FURTHER RESOLVED THAT:

          any acts authorized by these Resolutions but performed before their 
          passage are ratified, and

          these Resolutions remain effective and Buyer may rely on them until 
          it receives written notice of their revocation, but that notice will 
          not affect any of Seller's agreements or commitments then 
          effective."

I ALSO CERTIFY that the officers or agents above are duly elected or 
appointed by Seller and hold the positions opposite their names and that 
their signatures are true and that the Resolutions are effective and have not 
been modified or revoked.


/s/ Henry V. Morgan                                   August 28, 1998
--------------------------------------------          --------------------
(signature) Assistant Secretary or Secretary          Date

<PAGE>

                           SCHEDULE OF DUE DATES
                                      TO
                          NOTE PURCHASE AGREEMENT
                        DATED AS OF AUGUST 20, 1998

<TABLE>
<CAPTION>
DUE DATE                     AMOUNT DUE
<S>                        <C>
August 7, 1998               $350,000.00
September 1, 1998            $350,000.00
October 1, 1999              $350,000.00
November 1, 1999             $350,000.00
December 1, 1999             $350,000.00
January 1, 1999              $350,000.00
February 1, 1999             $350,000.00
March 1, 1999                $350,000.00
April 1, 1999                $350,000.00
May 1, 1999                  $350,000.00
June 1, 1999                 $350,000.00
July 1, 1999                 $350,000.00
August 1, 1999               $350,000.00
September 1, 1999            $350,000.00
October 1, 1999              $300,000.00
TOTAL PURCHASED NOTE       $5,200,000.00

</TABLE>
       
<PAGE>

                     NOTE PURCHASE MODIFICATION AGREEMENT

     This Note Purchase Modification Agreement is entered into as of 
September 23, 1998, by and between Radius, Inc., (the "Seller") whose address 
460 Middlefield Road, Mountain View, California 94303 and Silicon Valley 
Financial Services, a division of Silicon Valley Bank ("Buyer"), whose 
address is 3003 Tasman Drive, Santa Clara, CA 95054.

1.   DESCRIPTION OF EXISTING INDEBTEDNESS: Among other indebtedness which may 
be owing by Seller to Buyer, Seller is indebted to Buyer pursuant to, among 
other documents, a Note Purchase Agreement, dated August 28, 1998 by and 
between Seller and Buyer (the "Note Purchase Agreement"). Capitalized terms 
used without definition herein shall have the meanings assigned to them in 
the Note Purchase Agreement.

Hereinafter, all indebtedness owing by Seller to Buyer shall be referred to 
as the "indebtedness" and the Note Purchase Agreement and any and all other 
documents executed by Seller in favor of Buyer shall be referred to as the 
"Existing Documents."

2.   DESCRIPTION OF CHANGE IN TERMS.

     A.   MODIFICATION(S) TO NOTE PURCHASE AGREEMENT, EFFECTIVE AS OF THE 
          DATE FIRST WRITTEN ABOVE:

          Section 2.2 of the Note Purchase Agreement is amended and restated 
          to read in full as follows:

          "2.2  Payment of Advance Amount. Buyer will pay Seller, on the 
          Purchase Date, the amount of One Million One Hundred Thousand and 
          No/100*****$1,100,000.00 (the "Initial Advance"). Upon payment by 
          Buyer to Seller of the Initial Advance, Buyer and Seller shall 
          execute a Schedule to this Agreement evidencing the receipt by 
          Seller of the Initial Advance. At one or more times after the 
          Purchase Date, Buyer shall, upon the request of Seller, advance 
          additional sums to Seller aggregating not more than Three Million 
          Sixty Thousand and No/100*****($3,060,000.00), (the "Additional 
          Advances"; the Additional Advances and the Initial Advance are 
          collectively called the "Advance Amount"). Upon payment by Buyer to 
          Seller of each Additional Advance, Buyer and Seller shall execute a 
          Schedule to this Agreement evidencing the receipt by Seller of such 
          Additional Advance."

3.   CONSISTENT CHANGES. The Existing Documents are each hereby amended 
wherever necessary to reflect the changes described above.

4.   NO DEFENSES OF SELLER. Seller agrees that, as of this date, it has no 
defenses against the obligations to pay any amounts under the Indebtedness.

5.   CONTINUING VALIDITY. Seller understands and agrees that in modifying the 
existing Indebtedness, Buyer is relying upon Seller's representations, 
warranties, and agreements, as set forth in the Existing Documents. Except as 
expressly modified pursuant to this Note Purchase Modification Agreement, the 
terms of the Existing Documents remain unchanged and in full force and 
effect. Buyer's agreement to modifications to the existing Indebtedness 
pursuant to this Note Purchase Modification Agreement in no way shall 
obligate Buyer to make any future modifications to the Indebtedness. Nothing 
in this Note Purchase Modification Agreement shall constitute a satisfaction 
of the Indebtedness. It is the intention of Buyer and Seller to retain as 
liable parties all makers and endorsers of Existing Documents, unless the 
party is expressly released by Buyer in writing. No maker, endorser, or 
guarantor will be released by virtue of this


                                       1

<PAGE>

Note Purchase Modification Agreement. The terms of this paragraph apply not 
only to this Note Purchase Modification Agreement, but also to any subsequent 
Note Purchase modification agreements.



This Note Purchase Modification Agreement is executed as of the date first 
written above.

SELLER:                                BUYER:

Radius, Inc.                           Silicon Valley Financial Services,
                                       a division of Silicon Valley Bank

By:    /s/ Henry V. Morgan             By:    /s/ [illegible]
       ---------------------------            ------------------------------
Name:  Henry V. Morgan                 Name:  [illegible]
       ---------------------------            ------------------------------
Title: Secretary                       Title: Vice President
       ---------------------------            ------------------------------


                                       2