ITS SBLK format - Revision history

Larsbrinkhoff: Unredirect ITS.

2023-09-06T05:33:59Z

Unredirect ITS.

Jnc: /* Symbol table */ +link

2022-04-06T15:08:20Z

‎Symbol table: +link

Jnc: +cat, links

2022-04-05T21:12:05Z

+cat, links

Larsbrinkhoff: Describe the ITS SBLK format.

2022-04-04T05:26:06Z

Describe the ITS SBLK format.

New page

The ITS '''SBLK''', or '''simple block''' format, was introduced with the Project MAC [[PDP-6]] MIDAS assembler and adopted in the transition to timesharing.

====CREATING AN SBLK FILE====

The HACTRN $Y and MACDMP/DSKDMP D$ command writes a core image file in SBLK format.

====OVERVIEW====

An SBLK file consists of five sections:
# RIM10 loader.
# Simple blocks.
# Start instruction.
# Symbol table.
# Start instruction.

====RIM10 loader====

An SBLK file traditionally starts with a paper tape RIM10 bootstrap loader ending with a ''''JRST 1''' instruction. The loader is now optional except for the JRST.

====Simple blocks====

The core image is stored in a series of zero-compressed blocks. A block starts with an AOBJN header:

{| class="wikitable
| 0-17
| 18-35
|-
| -''count''
| ''address''
|}

After the header follows ''count'' word to be stored starting at location ''address'.

A simple block is ended by a checksum. The checksum includes the header word. A new checksum value is computed from the old checksum rotated left one bit, added to the word.

====Start instruction====

After the simple blocks comes a start instruction which must have bit 0 cleared. Conventionally this is a JRST, but sometimes JUMPA is used.

====Symbol table====

The symbol table is optional and may be empty.

The table is stored as simple blocks with the ''address'' as zero. There are alternating words of SQUOZE symbol names and 36-bit symbol values.

====Repeated start instruction====

After the symbol table there is a repeated start instruction.

← Older revision		Revision as of 05:33, 6 September 2023
Line 1:		Line 1:
−	The [[ITS]] '''SBLK''', or '''simple block''' format, was introduced with the Project MAC [[PDP-6]] MIDAS [[assembly language\|assembler]] and adopted in the transition to [[time-sharing]].	+	The [[Incompatible Timesharing System\|ITS]] '''SBLK''', or '''simple block''' format, was introduced with the Project MAC [[PDP-6]] MIDAS [[assembly language\|assembler]] and adopted in the transition to [[time-sharing]].

	====CREATING AN SBLK FILE====		====CREATING AN SBLK FILE====

@@ Line 42: / Line 42: @@
 The [[symbol table]] is optional and may be empty.
-The table is stored as simple blocks with the ''address'' as zero.  There are alternating words of SQUOZE symbol names and 36-bit symbol values.
+The table is stored as simple blocks with the ''address'' as zero.  There are alternating words of [[SQUOZE]] symbol names and 36-bit symbol values.
 ====Repeated start instruction====

@@ Line 1: / Line 1: @@
-The ITS '''SBLK''', or '''simple block''' format, was introduced with the Project MAC [[PDP-6]] MIDAS assembler and adopted in the transition to timesharing.
+The [[ITS]] '''SBLK''', or '''simple block''' format, was introduced with the Project MAC [[PDP-6]] MIDAS [[assembly language|assembler]] and adopted in the transition to [[time-sharing]].
 ====CREATING AN SBLK FILE====
@@ Line 16: / Line 16: @@
 ====RIM10 loader====
-An SBLK file traditionally starts with a paper tape RIM10 bootstrap loader ending with a ''''JRST 1''' instruction.  The loader is now optional except for the JRST.
+An SBLK file traditionally starts with a paper tape RIM10 bootstrap loader ending with a ''''JRST 1''' [[instruction]].  The loader is now optional except for the JRST.
 ====Simple blocks====
@@ Line 32: / Line 32: @@
 After the header follows ''count'' word to be stored starting at location ''address'.
-A simple block is ended by a checksum.  The checksum includes the header word.  A new checksum value is computed from the old checksum rotated left one bit, added to the word.
+A simple block is ended by a [[checksum]].  The checksum includes the header word.  A new checksum value is computed from the old checksum rotated left one bit, added to the word.
 ====Start instruction====
@@ Line 40: / Line 40: @@
 ====Symbol table====
-The symbol table is optional and may be empty.
+The [[symbol table]] is optional and may be empty.
 The table is stored as simple blocks with the ''address'' as zero.  There are alternating words of SQUOZE symbol names and 36-bit symbol values.
@@ Line 47: / Line 47: @@
 After the symbol table there is a repeated start instruction.