00100	Dear Larry:
00200	
00300		In response to your  letter  of  December  22,  here  is  the
00400	promised  justification  and  a  report  on the present status of our
00500	project to build  a  high  speed  special  processing  unit  for  our
00600	computer system.
00700	
00800		Part  of the need for the processor is simply a need for more
00900	computing power which we  expect  to  get  even  greater  as  picture
01000	processing  and  list prcoessing programs now being completed go into
01100	use as subroutines of higher level processes.  In addition  to  this,
01200	the hand-eye and cart driving programs require high real time compute
01300	capacity.  Existing programs sometimes take a minute to  decide  what
01400	to  do, and while software improvements to this are possible, we also
01500	want to make more ambitious computations. The factor of 10 to  20  in
01600	speed   that   the  new  processor  will  make  in  special  hand-eye
01700	computations will make a big difference.
01800	
01900		The conditions mentioned in your letter are agreeable to  us.
02000	The  present  situation  with  regard to conservatism in design is as
02100	follows:
02200	
02300		1. Texas Instruments' S-series TTL logic is  being  delivered
02400	in  quantities  larger  than  those we will require, and the users we
02500	have talked to say it meets specifications.
02600	
02700		2. The cache memory situation has also  changed.   There  are
02800	now  three potential suppliers of the memory, namely: Cogar makes the
02900	ECL memory we were previously planning to use.   Monolithic  Memories
03000	has  TTL chips somewhat slower than the Cogar memory but considerably
03100	cheaper.  Texas Instruments has announced 256 bit TTL chips which  in
03200	our  application  would  be as fast as the Cogar, avoid having to use
03300	ECL circuitry, and which are very much cheaper than the Cogar memory.
03400	Our  present plan is to use the Texas Instruments chips which will be
03500	available in sample quantities in April and in production  quantities
03600	in  June.   If  we  do  this  the  only  use  of  ECL  will be in the
03700	accumulator memory and in the use bits memory in the cache, and there
03800	will  be  no  ECL signals in the back plane; they will be confined to
03900	single cards.  On the other hand, if the TI memory should turn out to
04000	be  unavailable,  either the Cogar or the Monolithic Memories devices
04100	could be used.
04200	
04300		The machine will be able to use TENEX.
04400	
04500		We are agreeable to making  half  of  the  resources  of  the
04600	machine  available  through the network.  However, this may require a
04700	degree of reliability and documentation of software resources  higher
04800	than  that  we  now  provide.   It  may  also  require more auxiliary
04900	resources such as secondary storage.  After the machine is working we
05000	can  see  what  augmentation the system requires for reliable network
05100	use.  We currently expect to be using TENEX.
05200	
05300		It is proposed to call the processor the "High Speed  Special
05400	Processing   Unit"   or   HSSPU.   With  this  attractive  name,  the
05500	designation "Foonly" will doubtless disappear.
05600	
05700	
05800						Sincerely yours,
05900	
06000	
06100						John McCarthy