[cctalk] Re: IBM 350 disk and 305 drum [WAS:RE: Re: Drum memory on pdp11's? Wikipedia thinks so....]

On Mon, 15 Apr 2024, Tom Gardner via cctalk wrote: Here's what info I have on the RAMAC, from multiple sources, but derived at least partially, if not entirely, from some of Tom Gardner's earlier posts. RAMAC 50 user disks (dummy disks at end to reduce turbulent buffeting) 100 sides, 100 user tracks per side (2 test only tracks on inside and outside) A RAMAC character has 8 bits: 1 start bit, 6 data bits, and 1 parity bit. - clarification by Tom Gardner & Joe Feng 5 sectors per track, 100 characters per sector - Grand total of 50 disks x 2 sides/disk x 100 user track/side x 5 sectors/track x 100 char/sector = 5,000,000 characters Claimed average access time 0.6 seconds, you define "average" movements ;-)) However, the "IBM 650 RAMAC - Manual of Operation - Preliminary Edition" states that the worst case seek, from inner track of top disk to inner track of bottom disk, was 0.8 seconds !! (I *really* want to see that!!) ) 2 heads, one for tracks on top side of each disk, one for bottom side - head assembly moves vertically to selected disk, then goes to selected track - about 200 bits per inch - the magnetic tape density of the period. 2 hp drive motor drives the disks at 1200 RPM, 1/3 hp motor at 3450 RPM drives clutches at 1000 RPM one revolution of fully locked clutch drives arm 6 inches either in/out or up down - 100 inches or 8.3 feet per second - 200 disks per second or 2000 tracks per second Wikipedia: RAMAC mechanism at Computer History Museum The IBM 350 disk storage unit, the first disk drive, was announced by IBM as a component of the IBM 305 RAMAC computer system on September 13, 1956.[8][9][10][11] Simultaneously a very similar product, the IBM 355 was announced for the IBM 650 RAMAC computer system. RAMAC stood for "Random Access Method of Accounting and Control." The first engineering prototype 350 disk storage shipped to Zellerbach in June 1956;[12] however, production shipment announced to begin "mid-1957"[13] may not have occurred until as late as January 1958.[14] Its design was motivated by the need for real time accounting in business.[15] The 350 stored 5 million 6-bit characters (3.75 MB).[16] It has fifty 24-inch (610 mm) diameter disks with 100 recording surfaces. Each surface has 100 tracks. The disks spun at 1200 RPM. Data transfer rate was 8,800 characters per second. An access mechanism moved a pair of heads up and down to select a disk pair (one down surface and one up surface) and in and out to select a recording track of a surface pair. Several improved models were added in the 1950s. The IBM RAMAC 305 system with 350 disk storage leased for $3,200 per month. The 350 was officially withdrawn in 1969. U.S. Patent 3,503,060 from the RAMAC program is generally considered to be the fundamental patent for disk drives.[17] This first-ever disk drive was initially cancelled by the IBM Board of Directors because of its threat to the IBM punch card business but the IBM San Jose laboratory continued development until the project was approved by IBM's president.[18] The 350's cabinet was 60 inches (152 cm) long, 68 inches (172 cm) high and 29 inches (74 cm) wide. The RAMAC unit weighs about one ton, has to be moved around with forklifts, and was frequently transported via large cargo airplanes.[19] According to Currie Munce, research vice president for Hitachi Global Storage Technologies (which acquired IBM's storage business), the storage capacity of the drive could have been increased beyond five million characters, but IBM's marketing department at that time was against a larger capacity drive, because they didn't know how to sell a product with more storage. None-the-less double capacity versions of the 350 were announced[8] in January 1959 and shipped later the same year. In 1984, the RAMAC 350 Disk File was designated an International Historic Landmark by The American Society of Mechanical Engineers.[20] In 2002, the Magnetic Disk Heritage Center began restoration of an IBM 350 RAMAC in collaboration with Santa Clara University.[21] In 2005, the RAMAC restoration project relocated to the Computer History Museum in Mountain View, California and is now demonstrated to the public in the museum's Revolution exhibition.[22] My own text, based on newspaper histories: In 1958, Nikita Khruschev visited USA, to try to de-escalet the cold war a little. When he was refused permission to go to Disneyland, Frank Sinatra offered to take Mrs. Khruschev to Disneyland, but that didn't happen. The secret service tried to make it up to him by arranging a tour of an IBM plant in San Jose where the RAMACs were being built. I have a RAMAC platter! It was acquired sometime before 1983 by Wilson Price (one of my cow- orkers) and we used it for decades to convince beginning computer students that there has been progress on size and capacity of disks. It is much too damaged to be restorable. So, I made a patio table out of it. It already has a specific bequest? in my will. -- Grumpy Ol' Fred cisin(a)xenosoft.com