comparing the SAS System under OS/2 and Microsoft Windows Which is right for you? Mark W. Cates SAS Institute Inc. Abstract As we enter into the 1990s, two operating systems are available to enhance productivity forcEersonalcomput­ ers and provide a future platform for PC software users. The two environments, OS/2 • version 1.3 and Microsoft Windows ® 3.0 provide fundamentally the same user interface and similar features, but the underly­ ing operating systems are radically different. Today, corporations large and small are deciding which operat­ ing system should be used in their organizations and for which applications. The platform for more powerful and mission critical applications is clearly OS/2. However, with the introduction and overwhelming accep­ tance of Windows 3.0, supporting DOS compatibility, a graphical user interface compatible with Presentation Manager, and access to extended and virtual memory, a large memory alternative to OS/2 is available. This paper discusses these two environments with respect to the SAS System. The paper presents the advantages and disadvantages of the operating systems, configuration issues, and future directions, with respect to the SAS System. Issues that are particularly important to the SAS System are described in detail. Finally, the implications of the new 32 bit OS/2 version 2.0 are presented. (In this paper, Microsoft Windows 3.0 will be referred to as an operating system. Actual~, Microsoft Windows is a layered operating environment that runs on top of the operating system PC DOS •. For purposes of this paper, the distinction between operating environment and operating system is not important.) SAS release status for OS/2 and Windows Version 6.06 of the SAS System has been in production for OS/2 1.2 and 1.3 Standard and Extended Edition, as well as Microsoft's OEM versions since November 1990. It supports all SAS version 6.06 products and procedures including SAS/ACCESS, SAS/AF, SAS/ASSIST, SAS/BASE, SAS/CONNECT, SAS/ETS, SAS/ FSP, SAS/IML, SAS/GRAPH, SAS/OR, SAS/STAT, and SAS/QC. At SUGI15 in Nashville (March 1990), the Institute announced the planned support for Microsoft Windows version 3.0, starting with the SAS System version 6.07 .. This release is planned for late 1991. Simultaneously, version 6.07 will be released on OS/2 version 1.3. The Institute is committed to both of these operating environments and believe that each environment is strategic to corporations, and thus will provide support for them with future SAS releases. The products released on each environment will be the same. The feature set of the procedures will be identical; the only difference in the releases will be advanced features that one environment may support that the other does not. The SAS catalog file format and the data set file format will be byte for byte identical across the two systems. SAS data sets and catalogs will be easily and immediate­ ly transferrable between the two operating systems by merely using the copy command. Every attempt will be made to support upgrades of the operating system such as Windows 3.1 and upgrades to OS/2 version 1.3. Complete hardware and software requirements for both systems can be obtained by calling Software Sales at the Institute. Comparing OS/2 and Windows with respect to the SAS System Memory management OS/2 version 1.x supports the architectural functions of the Intel 80286 processor which includes accessing up to 16 Meg of physical extended memory, and up to 1 Gigabyte of virtual memory used for segment swapping. OS/2 1.x executes faster on a 80386 or 80486 processor due to the increased processing power but does not take advantage of 32 bit processing or the advanced memory management facilities of the 80386. OS/2 is supported on a 80286 machine, but SAS performance on this processor is obviously marginal. For 393 OS/2 1.2 and 1.3, the SAS System version 6.06 recommends a minimum of 6 Meg of memory and 8 Meg for optimum performance of large applications like SAS/ASSIST and SAS/GRAPH. It Is important to note that problems are only limited by the amount of disk swap space and that adding additional extended memory will normally increase the limits of the system. Unlike SASPC DOS versions using Expanded Memory (EMS), the SAS System may take advantage of all additional extended memory for both executable code and program data. The increased memory available to applications is a substantial benefit provided by OS/2. Compared to PC DOS execution, the SAS System executes faster under OS/2. Although this is contrary to some reports concerning performance comparisons between PC DOS and OS/2, it holds true for SAS because of the performance loss SAS suffered on PC DOS. Under OS/2, SAS does not have to resort to disk intensive code overlays and costly unloading and loading of executable images. Additionally, the code generator that is used to execute data step and procedure code has been improved and optimized for the OS/2 environment. Windows 3.0 runs in three modes: Real mode, Standard mode, and Enhanced mode. Real mode is the native mode of the original IBM PC using an Intel 8088 microprocessor. Original versions of Windows ran in real mode as does PC DOS, and is provided primarily for compatibility of older Window applications. SAS under Windows does not and will not support real mode in any future release, since real mode limits the application to 1 Meg of memory. In Standard mode, Windows requires at least an Intel 80286 with at least 1 Meg of memory, or a 80386 with less than 2 Meg of memory. In this mode, Windows runs in protected mode which means the processor can address up to a maximum of 16 Meg of extended memory if available. Standard mode, however, is limited to the physical available memory. Once this memory is used by applications, Windows memory management will move and discard program segments to attempt to manage the memory. However, swapping. of seg­ ments to disk to obtain virtual memory is not performed in standard mode. Therefore, adding more extended memory up to a maximum of 16 Meg is necessary to increase performance and overcome memory limitations for an application like SAS. Standard mode allows an application to execute faster than Enhanced mode because it does not rely on slower virtual device drivers that Window~,uses in enhanced mode. Enhanced mode requires an Intel 80386 or 80486 processor and at least 2 Meg of .extended memory. This is the most optimal mode for Windows and for power users. In this mode, the processor can once again access up to a maximum of 16 Meg of extended memory. However, Windows memory management takes advantage of the 80386 memory management paging features to "page" in and out 4 k byte blocks. When physical memory has been filled, the paging process begins. Only when all the virtual address space on disk has been used, does Windows discard program segments. (Discarded program segments are required to be reloaded and relocated, and thus discarding is slower than paging.) Enhanced mode can be misleading, especially to power users. A little published fact about Windows enhanced mode is that the virtual paged memory Is limited to approximately four times the amount of physical memory. This is a system limit, not a per task limit. For example, on a machine with 4 Meg of memory, Windows enhanced mode will provide the entire system including all applications running, with an address space up to 16 Meg (4 x 4) of memory, assuming that this amount of disk space is available in either the temporary or permanent swap file. This fact can easily dispell the belief that Windows virtual memory provides the same function and benefit that OS/2 does, just because both run in protected mode. The reason Windows limits the paging to four times physical memory is to prevent a large portion of the physical memory from being used by in-memory page tables. Another advantage of enhanced mode is that Windows uses .the virtual 86 mode of the 80386 processor to allow multiple DOS sessions to run in windows concurrently. This feature is more important for DOS programs. However, running multiple DOS shells can cause instability In DOS because DOS Is not reentrant. SAS version 6.07 will support only standard and enhanced mode. Both modes mode will require at least 6 Meg of memory and additional memory would increase performance. The system will run with less memory in enhanced mode, with a performance degradation. Multitasking and the Security of applications Perhaps the most important distinction between OS/2 and Windows is the method in which multitasking is accomplished. OS/2 is a powerful operating system that supports preemptive, time sliced multithreading 394 and multitasking. For example, there are features in the operating system to support multitasking such as threads, semaphores, signals, priority, separate address space, and a tasked based file system. In addition, OS/2 provides a robust environment for an application like SAS. Applications code and data are protected from being overwritten by other applications. To a large and sophisticated application such as SAS, this is a very important feature of an operating system .. Windows on the other hand, was designed to be compatible with the original Windows programming model of earlier releases, real mode Windows 2.x. Multitasking is not preemptive, but cooperative. Applications must be very well behaved and must yield execution of the application at designated points in order for the system to achieve the appearance of multitasking.