On 22 January 2018 at 09:51, R.S. <[email protected]> wrote: > I'm looking for some reference describing track format of CKD disk. > > What I know is > Index Point - Home Address - R0 - other Rn > > Some questions: > 1. IP is just a "start of track", contains no data - Y/N ? > 2. What is a format of HA? > 3. What is a format of R0? > 4. What is a format of Count field? How long is it? Is it 10 bytes? > 5. What is maximum length of K and D? > > Any documentation?
A good place to start is http://bitsavers.org/pdf/ibm/38xx/3880/GA26-1661-9_3880_Storage_Control_Description_Sep87.pdf Of course this is 30+ years old, but almost nothing has changed. Extended format (which you seem to be interested in) is not covered. But this book is good because if covers not only the data layout, but the format and rules for the CCWs to use the disk devices, the various status presentations Three stages of DASD programming, all described pretty well in the book, though not laid out historically: Early (S/360 2311, 2314, etc.). Selector channel (one active channel program at a time). Typical Read channel program has standalone SEEK, then when that finishes, SEEK again, Set File Mask, SEARCH, READ. A few strange DASDs like 2321 datacell, 230x drum/fixed head disks, all with quirks. RPS (S/370 3330, 3350) Block Multiplexor channels. Control unit can disconnect from the channel during seek and while the right spot on disk comes around, then reconnect. During this disconnection some other data transfer can proceed. You manage the rotational position with Get/Set Sector CCWs, and your channel program is suspended until CU reconnection. ECKD (3380, 3375, 3390) 3 MB/s channels "data streaming". New CCWs like Define Extent. Key point: 99% upward compatible. Your channel program written in 1968 for 2311 can run in 2018 on a 3390. Perhaps not optimal, but... Can any other architecture say that? I don't know how Extended format interacts with drives and CCWs. Maybe not at all... Do I hear Lynn Wheeler's keyboard clicking yet? Tony H. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO IBM-MAIN
