The table below lists the MVS control blocks that are emulated by MSS and specifies any differences between the non-mainframe versions and the mainframe versions.
| Name | Description | Differences from mainframe |
| IHAACEE | Accessor Control Element | ACEEVRSN is set to 2 |
| IHAASCB | Address Space Control Block | |
| IHAASVT | Address Space Vector Table | |
| IHAASXB | Address Space Extension Block | |
| CVT | Communication Vector Table | CVTTOD is set to X'20', indicating that the Time Of Day clock is operational.
CVTMVSE - the X'80' bit in CVTDCB is always on, indicating that you are running under MVS/XA or later. CVT4MPS - the X'04' bit in CVTDCB is on (indicating that you are running on System/360 Model 65 MP) only if the MVS control blocks are above the 16MB line (that is, all three-byte addresses are stored as four-byte addresses in the same location). CVTDATE is set with the century number (that is, it uses "0cyyddds" format, where "c" is century number - 0 for 20th, 1 for 21st, etc.) |
| CVT | CVT Prefix | The CVT prefix is set to all binary zeros. |
| IHACDE | Contents Directory Entry | One "null" CDE is allocated. So it appears to be using a program for which the load module has not been loaded. |
| IDADDSA | Dynamic Storage Area (FSA - First Save Area) | This is an 88-byte save area pointed to by TCBFSA. It is used as the TCB First Save Area. |
| IEFJFCBN | Job File Control Block | |
| IEZJSCB | Job Step Control Block | |
| IHAPSA | Prefixed Save Area | The X'01' bit in byte 7 (the first byte being byte 0) is on only if the MVS control blocks are above the 16MB line (that is, all three-byte addresses are stored as four-byte addresses in the same location). |
| IEESMCA | SMF Control Area | SMCASID is set to 'MSTR'. |
| IDADTCA | Task Communication Area |
The PRV address is always zero. The storage overflow routine does not provide overflow segments; it merely abends with the abend code S80A. You must ensure that the ISA setting is adequate for your application. |
| IDADTCA | TCA Prefix | |
| IKJTCB | Task Control Block | The TCB protect key is set to key 8. |
| IEFTIOT1 | Task I/O Table | A maximum of 256 TIOT entries (representing the first 256 DDs in the job step) are supported. |